Dubois And Beyond

In the late 19th and early 20th centuries, there were plenty of scientists who held to the notion that the cradle of humankind would be found in Africa. But some, like Ernest Haeckel and Eugene Dubois, saw similarities between humans and orangutans of Indonesia and anticipated that human origins occurred there. Eugene Dubois was an extraordinary character in the history of human origins science. He packed up his family and his life, and moved to the Dutch East Indies on, what seemed like to his colleagues, a fanatical hunch that he would discover the "missing link" there. But in 1891 he proved them all wrong by discovering hominin fossils on the island of Java. After three years of analysis, he dubbed his find Pithecanthropus, which combines the Greek for both ape (pithekos) and man (anthropos). His find would later be renamed Homo erectus, a species which had a humanlike body but a smaller more ape-like brain. Many subsequent expeditions beginning in the 1920s recovered many more remains of H. erectus from other Indonesian sites as well as the famous "Peking Man" site of Zhoukoudian, China, that has produced over thirty individuals between 500 and 250 Kya.

Much more ape-like human ancestors than Dubois' fossils were unheard of until 1924 when Raymond Dart analyzed a small skull with a fossilized brain, or endocast, known as the "Taung Child" from Sterkfontein Cave, South Africa. The specimen was more primitive than H. erectus and supported the African origins hypothesis. He named the remains Australopithecus africanus, meaning "southern ape man from Africa." Critics as well as supporters of Piltdown Man's place in human evolution argued that the skull was much too ape-like to belong to the human lineage. But, Dart showed that even though it did not have identifiable features that an adult would offer, the Taung Child had humanlike traits in the teeth and skull that differed from apes.

By 1959, Robert Broom had already recognized robust australopith fossils (today called the genus "Paranthropus") from South African cave sites, but a nearly complete skull found by Louis and Mary Leakey in 1959 made a much bigger splash. The Leakey's discovery of OH 5 from Olduvai Gorge, Tanzania, showed little sign of deformation and had a complete face. Immediately it was nicknamed "Nutcracker Man" and this find, after nearly twenty years of searching for human fossils led to a cascade of discoveries of more hominin fossils and stone tools from Olduvai Gorge including many specimens of early Homo.

The contribution from Louis Leakey (1903-1972) and Mary Leakey (1913-1996) to human evolutionary studies marks the beginning of the modern age of paleoanthropology because they immersed themselves in Africa as explorers and excavators, dedicated to the discovery of human origins. They found numerous sites. They inspired and literally started numerous careers of other scientists in search of human origins and evolution. They were excellent at publicizing their remarkable finds. They included local people in their expeditions and research. And most importantly, they solidified East Africa as the cradle of humankind.

Richard Leakey and Meave Leakey took over Louis and Mary's tenure in Kenya and continue to find exciting fossils today. Once it was established that Kenya and Tanzania are treasure troves of hominin sites, paleontologists began to discover a wealth of material in Ethiopia as well. 1974 marked the year of Donald Johanson's discovery of the Australopithecus afarensis skeleton called "Lucy" which was the most complete early hominin known to science at the time. Back in Kenya, during the 1970s, 1980s, and 1990s, a particularly successful group of paleontologists, nicknamed the "Hominid Gang," brought in a steady stream of hominin fossils. The team led by Richard Leakey (Louis Leakey's son), Alan Walker, Meave Leakey, John Harris, and Kamoya Kimeu collected numerous skulls and postcranial bones of Homo erectus, Homo rudolfensis, Homo habilis, Paranthropus boisei, Paranthropus aethiopicus. In 1985 they hit fossil pay dirt with the most complete early hominin skeleton ever found, a H. erectus boy called the "Nariokotome boy" or the "Turkana boy," named after the site and lakeshore where he was discovered.

Details of many of the most important hominin discoveries, especially more recent finds, are discussed in Chapter 3 where each hominin species is described. --

Missing Links

There will always be missing links or gaps in the fossil record where we expect to find transitional forms. Organisms from fungus to fish to fishermen have evolved adaptations for recycling carcasses into energy, preventing the majority of organisms from fossilizing. The notion of "missing links" is perpetuated because each time a fossil discovery fills in a gap in the fossil record, two more gaps are created. Then once fossils are found to fill those gaps, four more are created, and so on (Figure 1.4).

Opponents of evolution use this seemingly endless quest for missing links to argue against evolution's credibility and paleontology's productivity. This misunderstanding is probably best termed "mything links" because there are, indeed, countless transitional forms on record from birds with teeth and bony tails (Archaeopteryx), to whales with little legs (Ambulocetus), to apes that walk upright (Australopithecus).

The terms "missing link" and "transitional form" are highly misleading as well. They imply that the organism was not well adapted and that it was merely waiting or even striving to eventually evolve into a modern form. They are also misinterpreted to mean that ancestral forms are somehow equal mixes or blends of their modern descendents.

Figure 1.4 When Eugene Dubois found H. erectus he created room for two more missing links (above). One between H. erectus and humans and a second older, more primitive link joining H. erectus with the last common ancestor between humans and chimpanzees (LCA). Eighty years later, the A. afarensis skeleton called "Lucy" filled in the latter hole (below), getting one link closer to the chimp-human ancestor, "???", and to the other end of the chain at living chimpanzees. This idea of missing links can be misleading, however, because evolution is a branching process, not a blending or linear one. H. erectus is considered a missing link or a transitional form but it is not a blend of chimpanzees and humans, since it evolved after the split of the two lineages. Illustration by Jeff Dixon.

Figure 1.4 When Eugene Dubois found H. erectus he created room for two more missing links (above). One between H. erectus and humans and a second older, more primitive link joining H. erectus with the last common ancestor between humans and chimpanzees (LCA). Eighty years later, the A. afarensis skeleton called "Lucy" filled in the latter hole (below), getting one link closer to the chimp-human ancestor, "???", and to the other end of the chain at living chimpanzees. This idea of missing links can be misleading, however, because evolution is a branching process, not a blending or linear one. H. erectus is considered a missing link or a transitional form but it is not a blend of chimpanzees and humans, since it evolved after the split of the two lineages. Illustration by Jeff Dixon.